Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

can be accomplished with one system call when Oracle uses the Oracle Disk
Manager I/O interface. This interface reduces the number of system calls
performed to accomplish the same work, reducing the number of user space/kernel
space context switches.
About avoiding duplicate file opens
Oracle Disk Manager allows files to be opened once, providing a “file identifier.”
This is called “identifying” the files. The same file identifiers can be used by any
other processes in the Oracle instance. The file status is maintained by the Oracle
Disk Manager driver in the kernel. The reduction in file open calls reduces
processing overhead at process initialization and termination, and it reduces the
number of file status structures required in the kernel.
About allocating contiguous datafiles
Oracle Disk Manager can improve performance for queries, such as sort and
parallel queries, that use temporary tablespaces. Without Oracle Disk Manager,
Oracle does not initialize the datafiles for the temporary tablespaces. Therefore,
the datafiles become sparse files and are generally fragmented. Sparse or
fragmented files lead to poor query performance. When using Oracle Disk Manager,
the datafiles are initialized for the temporary tablespaces and are allocated in a
contiguous fashion, so that they are not sparse.
About Oracle Disk Manager and Oracle Managed Files
Oracle9i or later offers a feature known as Oracle Managed Files (OMF). OMF
manages datafile attributes such as file names, file location, storage attributes,
and whether or not the file is in use by the database. OMF is only supported for
databases that reside in file systems. OMF functionality is greatly enhanced by
Oracle Disk Manager.
The main requirement for OMF is that the database be placed in file system files.
There are additional prerequisites imposed upon the file system itself.
OMF is a file management feature that:
■ Eliminates the task of providing unique file names
■ Offers dynamic space management by way of the tablespace auto-extend
functionality of Oracle9i or later
OMF should only be used in file systems that reside within striped logical volumes,
which support dynamic file system growth. File systems intended for OMF use
must also support large, extensible files in order to facilitate tablespace
auto-extension. Raw partitions cannot be used for OMF.
Using Veritas Extension for Oracle Disk Manager
About Oracle Disk Manager and Oracle Managed Files
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